Lamp unit power supply system

ABSTRACT

A power supply system for illuminating an LED lamp unit  5,  having a normal mode of operation in which a mains input  4  of a driver  3  of the LED lamp unit is supplied by mains power  1,  and an emergency mode of operation, in which the LED lamp unit is supplied by a charge storage device  19,  is disclosed. The system includes an emergency mode converter  21  operable to step-up the voltage from the charge storage device and to supply the mains driver input for illuminating the LED lamp unit.

TECHNICAL FIELD

The present invention relates to power supply system and method for illuminating an LED lamp unit, having a normal mode of operation in which a mains input of a driver of the LED lamp unit is supplied by mains power, and an emergency mode of operation, in which the LED lamp unit is supplied by a charge storage device.

BACKGROUND TO THE INVENTION

Various arrangements for lighting systems are known which provide both conventional and emergency lighting. Such emergency lighting is intended to be activated when the conventional lighting is no longer operative because the direct mains supply to the conventional lighting is no longer available or malfunctions. Emergency lighting is typically powered by a battery or other energy storage device. Conventional lighting is controlled by an on/off switch by means of which a user (or control system) can control whether the lighting is illuminated or not. Generally, emergency lighting is intended to be automatically illuminated when the absence of mains power or the malfunction of mains power for the conventional lighting is detected in some way. Emergency lighting may be used to allow escape from buildings that would otherwise be in darkness due to the inoperativeness of the conventional lighting.

A lighting system comprising emergency lighting and conventional lighting may be considered to have two operating modes. In a normal mode, when the direct mains supply is operating normally (within the normal voltage range), a switched mains input, controlled by an on/off switch, is monitored, and the lamp is illuminated or extinguished in dependence upon the switched mains input In an emergency mode, when the mains supply is not available or is malfunctioning (is outside the normal voltage range), the lamp is illuminated automatically, irrespective of the status of the switched mains input, using power from a battery or other storage element.

Emergency lighting and conventional lighting may share components. For example, the same lamp (such as an LED also called Light Emitting Diode, lamp unit) may be used for both conventional and emergency lighting. Other components may also be shared. However, known arrangements, where the same LED lamp unit is used in both the normal and emergency modes, require a separate driver to drive the LED lamp unit from the battery in the emergency mode, in addition to a mains driver for driving the LED lamp unit from the mains in the normal mode. Separate drivers are used because the battery and mains supplies have very different characteristics. Providing two drivers is disadvantageous for cost and space reasons. Also, the requirement for a separate driver to drive the LED lamp unit from the battery in the emergency mode makes it difficult to add emergency mode functionality to an existing lighting system.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a power supply system for illuminating an LED lamp unit, having a normal mode of operation in which a mains input of a driver of the LED lamp unit is supplied by mains power, and an emergency mode of operation, in which the LED lamp unit is supplied by a charge storage device, characterised in that the system includes emergency mode converter means operable to step-up the voltage from the charge storage device and to supply the mains driver input for illuminating the LED lamp unit.

The charge storage device may be a battery or a capacitor.

The emergency mode converter means may comprise a boost converter, advantageously an isolated boost converter, that provides a DC output at normal mains level so that it enables a normal LED driver to be powered off the charge storage device for the emergency duration. The emergency mode converter means may comprise a boost converter, advantageously an isolated boost converter, that provides a DC output at a level different to normal mains level but which nevertheless enables a normal LED driver to be powered off the charge storage device for the emergency duration.

The emergency mode converter means may comprise instead of a boost converter a fly-back or forward or push-pull or half-bridge converter or buck-boost or a SEPIC (single-ended primary-inductor converter) converter.

The system may include controllable switch means operable to selectively provide mains power to the mains input of the driver in the normal mode and power from the charge storage device to the mains input of the driver in the emergency mode. In this way, the driver and the lamp unit may be powered in both the normal mode and the emergency mode. The emergency mode converter may be controlled in a way that a fixed discharge current of the charge storage device can be achieved.

Either signalling such as DALI or automatic detection of the DC rail may be used to reduce the power in the mains LED driver if desired, when power is supplied from the charge storage device. The embodiment provides an advantage of flexibility and fast time to market by using existing LED drivers (converters) during the emergency mode.

In another aspect, the present invention provides a power supply method for illuminating an LED lamp unit as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention an embodiment will now be described by way of example, with reference to the accompanying drawings, in which FIG. 1 shows schematically the elements of a lighting arrangement that provides both a normal mode and an emergency lighting mode.

DETAILED DESCRIPTION OF EMBODIMENT OF THE INVENTION

FIG. 1 shows schematically the elements of a lighting arrangement that provides both a normal mode and an emergency lighting mode. A direct mains AC supply 1 provides power in the normal mode to a driver 3 optimised for use with the mains supply 1 (e.g. 230 volts, 50 Hz in the EU).

The driver 3 is supplied with power at a mains input 4 when a mains relay 7 is closed. A control part 8 monitors the mains AC supply 1. If the control part 8 detects that the mains AC supply 1 is interrupted, or if it is determined to be malfunctioning (operating outside an acceptable range of values), the control part 8 may provide an appropriate signal to relay control line 9 to open the mains relay 7 and to close an emergency relay 11. The emergency relay 11 allows the lamp 5 to be driven in an emergency mode. The driver 3 is preferably an independent driver which is only connected to the mains AC supply through the mains relay 7 which is closed when mains AC supply is available. In a preferred embodiment there is no additional link between driver 3 and emergency lighting module 12.

To provide the emergency mode, an emergency lighting module 12 includes, in addition to the mains relay 7, relay control line 9 and emergency relay 11, a smoothing input filter 13, a rectifier 15 (typically a bridge rectifier), a battery charger 17 (a SELV, Separated Extra Low Voltage, isolated DC-DC converter, a flyback converter, for example), a battery 19 and a step-up converter 21. The battery charger 17 may provide galvanic isolation between the AC mains supply 1 and the battery 19 for safety reasons. The converter 21 may likewise provide galvanic isolation of the battery 19 from the lamp 5.

The battery 19 may comprise a plurality of cells. Another energy storage device may be used instead of the battery 19.

When the mains AC supply 1 is operating normally (and the lamp 5 is powered by the AC supply 1), the battery 19 may be charged (continuously or when required) by the battery charger 17. The mains relay 7 is closed when mains AC supply 1 is operating normally and the LED is fed by the Standard LED driver 3. When the control part 8 detects that the AC supply 1 is interrupted (or malfunctioning), the emergency relay 11 is closed (the mains relay 7 is opened), and the driver 3 illuminates the lamp 5 using power from the battery 19.

As discussed above, the lighting arrangement shown in FIG. 1 includes the control part 8 which detects when the AC mains supply 1 is present and operating correctly—such as when the AC mains supply 1 presents a voltage higher than a certain threshold (187 volts in a 230 volt nominal supply, for example). When the AC mains supply 1 is present and operating correctly, the AC supply 1 provides power to illuminate the lamp via closed relay 7. Power from the AC mains supply 1 is also provided to battery charger 17 to charge the battery 19 (or to keep the battery 19 fully charged). The control part 8 is preferably a part of the emergency lighting module 12.

The battery charger 17 is constituted, in this example, by a so-called flyback converter which exhibits, on the one hand, a transformer T with a primary winding L_(P) and a secondary winding L_(S) and also, on the other hand, a controllable switch S₁. In known manner, by an appropriate alternating opening and closing of the switch S₁ the energy made available by the AC mains supply 1 is transmitted to the secondary side of the flyback converter and utilised for the purpose of charging the battery 19. The transmission of energy takes place in the open state of the switch S1, wherein for this purpose a diode D₁ is furthermore provided on the output side of the flyback converter. The battery charger 17 is constituted by an isolated DC-DC converter. Instead of a flyback converter other isolated converter topologies like a forward converter or an isolated SEPIC converter may be used as well.

The control part 8 also controls various aspects of operation of the driver 3, including the power supplied to the LED lamp 5—so that the level of illumination (dimming) can be varied.

The control part 8 monitors switched mains input 20, and, in the normal mode of operation, illuminates the LED lamp 5 (using the driver 3) when the switched mains input 20 is on.

The control part 8 may determine the status of the switched mains input 20 in any suitable manner. For example, it is known to apply the switched mains input 20 to a potential divider, and then to a voltage threshold detector with an isolation circuit, such as an opto-coupler. Typically, the switched mains input 20 is rectified by a rectifier before being applied to the voltage threshold detector and the isolation circuit. When the switched mains input 20 is on, the output of the isolation circuit will be a pulsed signal, the presence of which can be detected by logic within the control part 8. When the switched mains input 20 is off, the output of the isolation circuit will be a constant value (zero volts) and this can also be detected by logic of the control part 8. The control part 8 then operates the driver 3 and lamp 5 in accordance with the state of the switched mains input 20.

The lighting system may optionally comprise an interface 25, e.g. a DALI (Digital Addressable Lighting Interface), that is connected to a bus 26 (e.g. DALI bus), for intensity control (dimming) and/or for maintenance and service control. DALI is a communication protocol widely used in lighting systems. A two wire serial communication arrangement establishes a master/slave communication between a central DALI controller (not shown) and the lighting system control part 8 by setting low and high levels of voltages. Data are transferred between the DALI controller and lighting system control part 8, by means of an asynchronous, half-duplex, serial protocol over a two-wire differential bus, with a fixed data transfer rate of 1200 bit/s. The DALI data are transmitted using Manchester encoding. The protocol standard sets high levels as voltage differences high at 9.5V (either positive or negative) between the two wires. Low levels are set as voltage differences of less than 6.5V.

The converter 21 may comprise a flyback or forward or push-pull or half-bridge or isolated boost converter with a step-up characteristic and a SELV isolation barrier, whose input is connected directly to the battery 19. The converter 21 may comprise as an alternative variant a non-isolated topology as for example a buck-boost converter.

The converter 21 comprises an input part X. The input part X comprises a switch S₂ and a primary winding section N₁ which is connected in parallel across the battery 19. By operation of the switch S₂, the input part produces a rectangular output voltage. The time for which each of the switch is closed and the frequency of operation (opening/closing) of the switch is controlled by a driver controller (not shown).

The input part X of the converter 21 supplies an output part Y. The output part Y includes a secondary winding N₂ with a rectifier unit and a smoothing filter, e.g. a L (inductor) series C (capacitor) parallel filter, connected to it. The rectifier unit may be formed by a single diode or by full wave rectifier. The converter 21 may provide a DC voltage or an AC voltage on its output. In case of an DC output the output part Y may comprise a rectifier and smoothing filter as shown in the example. When the control part 8 detects that the AC mains supply 1 is interrupted or malfunctioning—such as when the mains AC supply 1 presents a voltage lower than a certain threshold (145 volts in a 230 volt nominal supply, for example) the control part 8 opens the mains relay 7, closes the emergency relay 11, and activates the converter 21. The converter 21 provides power to illuminate the lamp 5 from only the battery 19 via the closed emergency relay 11.

In accordance with an important feature of the embodiment, the converter 21 may provide an output at normal mains level so that the output can be applied to the same mains input 4 of the driver 3 as the AC mains supply 1 in the emergency mode. It is also possible that the converter 21 provides an output at a level different from the normal mains level but which is nevertheless sufficient so that the output can be applied to the same mains input 4 of the driver 3 as the AC mains supply 1 in the emergency mode. The same components of the driver 3 may be used in both the normal and emergency modes. The converter 21 may provide a DC voltage or an AC voltage to the mains input 4 of the driver 3. Optionally, the AC mains supply 1 may be applied to a rectifier unit and a smoothing filter (not shown) so that a smoothed DC voltage is applied to the mains input 4 of the driver 3 in the normal mode.

This has the advantage that a separate driver for driving the LED light unit 5 is not required in the emergency mode. Because the output of the converter 21 is at (or near) the normal mains level, it can be applied to the driver 3 as if it was the AC mains supply 1. No modification to the driver 3 is required to allow an emergency mode to be possible. This is advantageous if it is desired to add emergency mode functionality to an existing light installation. The emergency module 12 can be added to the existing installation (comprising the driver 3, which is normally powered by the AC mains supply 1, and the LED light unit 5)—and the existing driver 3 can be used in the emergency mode without modification.

The converter 21 may be controlled in a way that a fixed discharge current of the charge storage device 19 can be achieved. The discharge current of the charge storage device 19 can be controlled by the converter 21. Preferably the converter 21 is operated in a way where the discharge current of the charge storage device 19 is fixed or is depending on a given curve depending on the voltage or status of the charge storage device 19. Such control of the converter 21 of the discharge current of the charge storage device 19 can offer an optimised utilization of the charge storage device 19 according to the given capacity of this charge storage device 19 and/or depending on the expected or intended duration of the emergency mode.

Depending on the type of mains voltage detected on the direct mains input 1, the control part 8 may put the driver 3 into different operation modes, e.g. to illuminate the lamp 5 at a given intensity level. For example, if it is detected that the direct mains input 1 is absent or malfunctioning (emergency mode), the control unit may cause the driver 3 to lower the light intensity level of the lamp unit 5 (dimming) in order to reduce power consumption.

It is also possible the there is no DALI bus 26 and no control part 8. In such case the driver 3 can be formed to be able to monitor the voltage on the mains input 4 of the driver 3 and to detect a change of the mains input 4 by a detection of the type of voltage or amplitude of the voltage detected on the mains input 4 of the driver 3. For example the operation mode of the driver 3 can be changed to emergency mode in case where a DC voltage is detected on the mains input 4 of the driver 3. The driver 3 may be able to detect that it is supplied with a voltage at a level different from the normal mains level and may be able to automatically reduce the current or power supplied to the LED 5 in such case as can be detected as operation in emergency mode.

The dimming level may also be varied by signalling via the DALI interface 25 and DALI bus 26.

Although the embodiment uses a forward converter as emergency mode converter means 21, several other converter arrangements, e.g. a push-pull converter, are able to provide a suitable voltage output, and may be used in accordance with the invention. 

1. A power supply system for illuminating an LED lamp unit (5), having a normal mode of operation in which a mains input (4) of a driver (3) of the LED lamp unit (5) is supplied by mains power (1), and an emergency mode of operation, in which the LED lamp unit (5) is supplied by a charge storage device (19), the system includes comprising an emergency mode converter (21) configured to step-up the voltage from the charge storage device (19) and to supply the mains input (4) for illuminating the LED lamp unit (5).
 2. The system of claim 1, wherein the emergency mode converter (21) is configured to step-up the voltage from the charge storage device (19) to a similar voltage to that of the mains power in the normal mode or operation.
 3. The system of claim 1, wherein the emergency mode converter (21) comprises a: flyback; forward; push-pull; half-bridge; buck-boost or SEPIC converter.
 4. The system of claim 1, further comprising a controllable switch (7, 9, 11) configured to selectively provide mains power (1) to the mains input (4) of the driver (3) in the normal mode, and power from the charge storage device (19) to the mains input (4) of the driver (3) in the emergency mode.
 5. A power supply method for illuminating an LED lamp unit (5), having a normal mode of operation in which a mains input (4) of a driver (3) of the LED lamp unit (5) is supplied by mains power (1), and an emergency mode of operation, in which the LED lamp unit (5) is supplied by a charge storage device (19), method comprising providing an emergency mode converter (21) to step-up the voltage from the charge storage device (19) and to supply the mains input (4) to illuminate the LED lamp unit (5).
 6. The method of claim 5, wherein the emergency mode converter (21) steps-up the voltage from the charge storage device (19) to a similar voltage to that of the mains power in the normal mode of operation.
 7. The method of claim 5, wherein the emergency mode converter (21) comprises a: flyback; forward; push-pull; half-bridge; buck-boost or SEPIC converter.
 8. The method of claim 5, further comprising using a controllable switch (7, 9, 11) to selectively provide mains power (1) to the mains input (4) of the driver (3) in the normal mode and power from the charge storage device (19) to the mains input (4) of the driver (3) in the emergency mode. 